Dead bolt latches used on doors employ a backset adjustment by which movement or throw of a latch's security pin or bolt can be set during installation of the latch. The “backset” is the distance between the forward or front face of a stationary casing portion of the latch and a transverse axis about which a latch operator moves to extend and retract the pin or bolt. This measurement is generally standard for most latches and is equal to ⅜″ or 0.375″ (0.95 cm) for an industry standard range of motion of between 2⅜ ″ and 2¾″. The standardized construction permits a high degree of interchangeability between latches.
Within the latch industry, there is a need for latches which are quickly and easily adjustable between the two limits of backset measurements, it being understood that any adjustments are typically made by relatively unskilled workmen such as a homeowner, janitor or maintenance person, or the like. In U.S. Pat. No. 4,664,433 there is described a door latch construction in which a casing and bolt each include components one of which has a helical slot that engages a projection on another of the components. The slot and projection provide for longitudinal movement, in a helical manner, between a forward and rear backset position. While effective, this construction can be cumbersome for an unskilled person to adjust and obtain the proper backset.